Download a PDF article that concludes that "[t]he instructional schedule does affect student grades on the four AP Examinations in this 1998 study after they have been adjusted for group differences in student ability. The results from this study generally suggest that students, on average, obtain higher AP grades when instruction is given over an entire year rather than in a semesterized block schedule format. These results are consistent across the four AP Examinations and are found on 15 of the 16 comparisons between year-long and semester block courses. The remaining results differ by examination and subject."